In order to investigate changes in the work-hardening rate of a face-centered cubic superalloy as a function of temperature, tensile tests were conducted at temperatures ranging from room temperature to 1123K. A serrated flow behavior of the stress-strain curve, caused by dynamic strain-aging, appeared at temperatures ranging from about 673 to 1073K. A linear work-hardening behavior was observed, followed by fracture without appreciable dynamic recovery, at temperatures ranging from room temperature to 943K; where the dynamic strain-aging exhibited a peak, thus indicating that stage-III work-hardening did not occur below 943K. Transmission electron microscopic observations and phase stability considerations led to the conclusion that, within the temperature range where dynamic strain-aging operated, so-called Suzuki segregation into stacking faults which were bounded by Shockley partials could occur so that dislocation dissociation was extended, thereby causing suppression of cross-slip events. Since it was difficult for the stress-relief mechanism due to cross-slip to occur in the temperature range where dynamic strain-aging operated, deformation twinning became an alternative mechanism for reducing the internal stress which was increased by plastic deformation. It was proposed that dynamic strain-aging was here responsible for the higher work-hardening rate, and the occurrence of deformation twinning at high temperatures.

High Work-Hardening Rate and Deformation Twinning of Co-Ni-Based Superalloy at Elevated Temperatures. A.Chiba, X.G.Li, M.S.Kim: Philosophical Magazine A, 1999, 79[7], 1533-54